Supernova 2011b Gradually Fading 122
An anonymous reader writes "The recent stellar explosion known as 'supernova 2011b' is gradually fading after outshining its host galaxy for over a month. The explosion first flared up in early January, and peaked at magnitude 12.9, putting it within the reach of many amateur telescopes. The host galaxy, NGC 2655, lies 64 million light years away, meaning that the star exploded while the dinosaurs still roamed the planet. My own sketches are available at gkastro.tk/."
Dinosaurs? (Score:5, Informative)
I thought the dinosaurs died out 65 million years ago?
That means they were already dead for a million years, 64 million years ago.
Re:Damn it! (Score:5, Informative)
http://www.novaresource.org/ [novaresource.org]
Re:Damn it! (Score:5, Informative)
If only I would of found out about the supernova back in January! Never seen one before and it is possible that there won't be another within my lifetime.
Don't worry. If you accept supernovas like this one, that's in a different galaxy than ours, there are plenty of them somewhere in the universe every year. It's only if you want one in our galaxy that you have to wait, since the frequency is on the order of one per century.
There was one in the Large Magellanic Cloud back in 1987, easily visible to the naked eye (if you were in the southern hemisphere).
Actually, it's getting to be time we had one in our galaxy. But unfortunately, they don't seem to be scheduled anywhere that we can easily read. The schedule has probably been on file at our local planning department in Alpha Centauri for 50 of our years, but we can't be bothered to make the short trip to check it out. So we'll just have to keep looking up at the night sky until something new appears there.
Re:Dinosaurs? (Score:2, Informative)
NO. In our frame of reference it happened ~64 million years ago and we are just now finding out about it. The only frame of reference where it occurs "now" is the frame of reference of the photons traveling at the speed of light. Relativity doesn't work that way.
Re:rhetorical question (Score:5, Informative)
No, it's not; you're absolutely right. In our frame of reference, it just happened recently -- and while you could say, "yeah, but in the star's reference frame, it happened tens of millions of years ago," it's also true that in the star's reference frame, dinosaurs on Earth are just now going extinct. IOW, it's not a very meaningful reference frame from where we're sitting.
The "well, actually it happened X million years ago" comments that seem to accompany every /. story about some distant, recently observed astronomical event are an example of the classic nerd failing of assuming that because we're smart people who know a lot about a lot of things, we're geniuses who know everything about everything. And I'm probably as guilty of it as anyone else ...
Re:rhetorical question (Score:4, Informative)
Furthermore, the thought that "the event really occurred X years ago" seems to assume a universal standard of time, independent of the location and velocity of the observer, by which far apart events can be ordered. But time is not like that is it?
Well, yes and no. That can be true for events viewed by observers moving at a sufficiently high speed relative to each other. But this remote galaxy is probably only moving relative to us at a few hundred km/sec, which is a sufficiently slow speed that (for our purposes here) they can be considered in the same reference frame. In such cases, comparing time is simple (though perhaps not doable to nanosecond accuracy).
An example on a smaller time scale: Light moves about 299 792 458 km in a second, and the Earth's diameter is about 12,742 km. So the Earth is approximately 43 light-milliseconds in diameter. Yet it's possible (if not trivial) to synchronize clocks on the Earth's surface to nanosecond precision, and there are communication protocols that keep them synchronized. The GPS system wouldn't work if this weren't possible, and those satellites are moving relative to us even faster than the Earth's surface or this supernova.
One interesting use of this where such precision is critical is that astronomers sometimes combine the data from telescopes scattered around the world to make a large telescope with an effective aperture as wide as the Earth. Doing this requires measuring the arrival time of light waves with precision much better than 43 microseconds. The better precision, the less fuzzy the resulting images are.
This is possible because all those telescopes have very small velocities relative to each other. The max relative speed of two objects on the Earth's surface is twice the rotation speed of a spot on the equator. That's such a small fraction of the speed of light that it's negligible, and they can be treated as being in the same frame to many more than 10 decimal places.
If a remote astronomical object were moving at .99c relative to us, calculating relative times from both viewpoints would be complex and a bit strange to most people. But at relative speeds of .000001c or less, as with NGC 2655 and our galaxy, comparing times to within a few years is simple and straightforward (as astronomers measure such things ;-).
Re:Damn it! (Score:4, Informative)
It's not that bright, you need a good telescope to see it. Not that rare either, one hits 12th magnitude once or twice a year. It looks like just another very dim star in the scope. The difference between January and now isn't much at all.
Now, if one were to pop off in our part of the galaxy it would be news. Astronomers have been waiting for one visible to the naked eye for about 400 years.
Here's a list of current supernovae:
http://www.rochesterastronomy.org/supernova.html [rochesterastronomy.org]
Re:rhetorical question (Score:5, Informative)
That's not correct. Or at least that's not how simultaneity and past/present/future are defined in relativity, which seems to be what you're referring to with "frame of reference". I suppose you could define 'now' in that way... but that's not how it's defined in modern physics.
In our inertial reference frame, it happened ~64 million years ago. In the star's reference frame, it also happened ~64 million years ago. It's true there is no such thing as a universal reference frame, so one can certainly construct inertial reference frames (e.g. with large velocities relative to us) where the event occurred at different times. Even 'now' (in that reference frame). But the velocity difference between us and the supernova is modest (in the grand scheme of the universe) and thus our two references frames roughly agree about simultaneity and so on.
It's a strange misconception that people interpret relativity to mean that all space-time events on our past light-cone [wikipedia.org] are 'now'. Relativity doesn't say that. It includes a well-defined concept about what is in the past, what is in the future, and the boundary between them being 'now'. We are not immediately aware of all space-time events on the 'now' plane... because it takes time for their signals to reach us. But when we receiving signals we are able to reconstruct and deduce what happened at previous moments. It is true that inertial reference frames do not agree on what 'now' means, and thus don't agree on simultaneity. But within a particular inertial reference frame, there is a meaningful concept of 'now'.
Again, I suppose you could define 'now' in such a way, but it's not at all useful to think of the big bang happening 'right now' as we look far out into space. It makes much more sense to think in terms of it having happened 13.7 billion years ago, and we're only now receiving signals from the afterglow of the big bang from distant regions of space.
Re:Dinosaurs? (Score:5, Informative)
Sorry AC, Light cone is the correct terminology when discussing relativistic phenomena. It has to do with how the posibility function looks when graphed; it creates a cone shaped region. anything inside the cone is observable at some point in the lifetime of that photon generating event, anything outside that cone is not observable.
The point that the GP was trying to drive home is that relativity outright rejects the notion of "standardized time", and also any notion of a "universal reference point" from which to observe without also suffering from relativistic effects.
This is because time is a variable under relativity, and because all objects are in motion, and thus subject to relativistic effects. Your suggested correction of "light sphere" may not look very spherical from a specific vantage point, due to non-uniform spacial curvatures interacting with that light.
Long story short, your correction is in fact, incorrect. Sorry.
Re:Wow Many amateur telescopes (Score:3, Informative)
Magnitude 12.9 is quite visible to a 254mm (10 inch) newtonian (dobsonian) telescope that would cost you less than $600 if you picked one up second-hand. The trick is familiarising yourself with the night sky to be sure you're looking at the correct dim dot. ;)
For thousands of dollars (and a lot of patience) you can discover them yourself using a computer controlled mount and a modest amount of aperture: Dave Grennan *discovered* a supernova from the outskirts of Dublin city using a 14 inch Cassegrain scope. http://www.science.ie/science-news/supernova.html [science.ie]
https://secure.wikimedia.org/wikipedia/en/wiki/Limiting_magnitude#In_amateur_astronomy [wikimedia.org]
Magnitude calculator: http://www.cruxis.com/scope/limitingmagnitude.htm [cruxis.com]
If only we could get more done about the horrible light pollution one wouldn't have to travel so far from urban areas.
Re:Wow Many amateur telescopes (Score:5, Informative)
Photographically it is well within reach of DSLRs equiped with a 200mm lens. I managed to go down to magnitude 17 (or 100 times less bright) and even fainter with a Canon 20D and a 200mm f/2.8 lens, placed on a tracking mount and exposed for about 2 hours (accumulated in exposures of a few minutes). I'm sure it would even lie within the limits of a 50mm lens. The problem becomes distinguishing it from the host galaxy.
Visually it was within reach of 4.5" beginner scopes at dark locations! These will set you back less than $200 nowadays. A $1000 12" would have produced very decent views of the SN together with it's host galaxy. There are a lot of telescopes of this size around. You obviously should take the time to visit a public observatory once.